This species is characterized by its slender habit with creeping stems that root at the nodes, its lanceolate leaves with the apex acute to shortly aristate, and its solitary sessile flowers. Some plants of this species have very small leaves (ca. 0.8 x 0.3 mm); these plants were included in this species by Mena, similarly to variation found in other species of Arcytophyllum, but may deserve further study now that more material is available. It is similar to Arcytophyllum muticum and Arcytophyllum aristatum. Mena separated Arcytophyllum filiforme and Arcytophyllum muticum by stipule and leaf form.

The name Hedyotis serpens has sometimes been synonymized with Arcytophyllum filiforme, but the type of that other name is quite different.